2-Part Epoxy Failing?

[Ferbz]

I've used 5min 2-part epoxy successfully and confidently for many years and have used a variety of different brands. Lately though, I have noticed parts on some of my previous builds coming loose! So far, two of my older builds have had suspensions coming apart where I have used 2-part epoxy to assemble them. One of the builds is about 5yrs old, the other build is over 20yrs old. All my other builds seem to be holding up fine (for the moment!). I'm thinking maybe I came across bad 'batches' of epoxy at the time of those builds? or maybe 2-part epoxy has a shelf life for it's strength/reliability? Or maybe there are epoxy brands that are more inferior than others? Any insight would be grateful. I'd hate to think that my builds will start deconstructing themselves over time even though I've used epoxy which is known to be a very strong, reliable adhesive 🤪 

[Ace-Garageguy]

5-minute epoxy is, in a word, garbage.

In general, the longer any epoxy takes to fully cure, the stronger it is.

The epoxy I usually use for modeling is out-of-date material made for full-scale aircraft work. I assure you...it does NOT fall off over time if used correctly.

It also requires 24 hours to cure at room temperature, and a further post-cure at elevated temperatures to achieve full strength. It costs $400 per gallon.

If you want good long lasting epoxy joints, use at LEAST the 30-minute stuff made for model airplanes.

AND CLEAN AND SAND THE AREAS YOU'RE APPLYING IT TO THOROUGHLY.

ANY epoxy applied to a shiny or contaminated surface is a recipe for failure.

EDIT: Inaccurate or inadequate mixing is more likely than a "bad batch" of material...but 6 months to a year is usually the longest you can really trust the hardware-store or hobby-shop stuff anyway.

Cheapo consumer grade epoxies allow for a lot of latitude in mixing proportions, but that negatively affects strength. Insufficient mixing also negatively affects strength...and mixing the 5-minute stuff is often rushed because it starts to set so fast.

Edited January 27 by Ace-Garageguy

[NOBLNG]

I have nowhere near as much experience as Bill with epoxy adhesives, but I wouldn’t think that it should ever fail in a static model situation? Like Bill said, mixing could be the issue? Any glue other than a solvent that “melts” the parts together is a mechanical joint that needs to bond to the surfaces. Roughing up the surface will give the glue something to key into. I prefer Permatex brand 5 minute epoxy over JB or Gorilla brand. JMO.

Edited January 27 by NOBLNG

[Chariots of Fire]

I've successfully used Bob Smith Industries 2-part epoxy for years and have found it to be durable.  Mixing is important as Bill has said.  The one material that it does not like that well is aluminum.  It works but not as well as on other surfaces.

[1930fordpickup]

5 minute epoxy does have a shelf life before it is mixed and cured. Once it is cured and on a shelf they should be fine. For parts to be falling apart now it may be your prep work, unless the epoxy was old. When the epoxy starts to get stiff just pushing it out of the tube, it is getting old.

.

[NOBLNG]

3 hours ago, 1930fordpickup said:

5 minute epoxy does have a shelf life before it is mixed and cured. Once it is cured and on a shelf they should be fine. For parts to be falling apart now it may be your prep work, unless the epoxy was old. When the epoxy starts to get stiff just pushing it out of the tube, it is getting old.

.

Yes, I bought some JB Weld 5 minute epoxy in the 4oz. bottles (thought it was a good deal?). I only used about 1/3 of it and the “Part A” resin has gone hard as a rock. I now prefer the syringe type dispensers, as there is no air pocket left in the container as it is used up.

[Mike 1017]

I just add a little more hardener. It wors for me

[StevenGuthmiller]

20 hours ago, Ace-Garageguy said:

5-minute epoxy is, in a word, garbage.

In general, the longer any epoxy takes to fully cure, the stronger it is.

The epoxy I usually use for modeling is out-of-date material made for full-scale aircraft work. I assure you...it does NOT fall off over time if used correctly.

It also requires 24 hours to cure at room temperature, and a further post-cure at elevated temperatures to achieve full strength. It costs $400 per gallon.

If you want good long lasting epoxy joints, use at LEAST the 30-minute stuff made for model airplanes.

AND CLEAN AND SAND THE AREAS YOU'RE APPLYING IT TO THOROUGHLY.

ANY epoxy applied to a shiny or contaminated surface is a recipe for failure.

EDIT: Inaccurate or inadequate mixing is more likely than a "bad batch" of material...but 6 months to a year is usually the longest you can really trust the hardware-store or hobby-shop stuff anyway.

Cheapo consumer grade epoxies allow for a lot of latitude in mixing proportions, but that negatively affects strength. Insufficient mixing also negatively affects strength...and mixing the 5-minute stuff is often rushed because it starts to set so fast.

Guess I’ve been pretty lucky.

I’ve got models assembled 10 years ago almost entirely with 5 minute epoxy, and they travel quite often.

Can’t remember ever loosing a part on any of them....except for when a trophy tipped over on the back of my ‘65 Fury, and in that case, there were more broken plastic parts than separated joints.

In all honesty, I’ve had FAR more problems with parts falling off that were glued on with CA glue.

To the point where I almost never use it any more.

 

 

 

 

Steve

Edited January 28 by StevenGuthmiller

[Ace-Garageguy]

1 minute ago, Mike 1017 said:

I just add a little more hardener. It wors for me

Epoxy is supposed to be mixed in specific proportions to harden correctly, and to achieve maximum adhesion.

High-performance epoxies even have to be mixed using a gram scale, often with only .5% deviation from the specified mix ratio being tolerable.

Adding a higher percentage than specified of one or the other component to epoxy negatively affects performance.

Polyester, on the other hand, can tolerate a somewhat higher or lower percentage of "hardener" (because it's technically a catalyst) but it doesn't make it stronger. It only adjusts the cure time relative to temperature.

[Ace-Garageguy]

1 minute ago, StevenGuthmiller said:

Guess I’ve been pretty lucky.

I’ve got models assembled 10 years ago almost entirely with 5 minute epoxy, and they travel quite often.

Luck probably doesn't have anything to do with it.

I'd assume, judging from the attention you give the rest of your work, that you use product that's not expired, you probably exercise care with your mix ratios, mix very thoroughly, and you may even rough up the areas to be bonded.

If you DON'T do those things, then yes, it IS luck.

[StevenGuthmiller]

7 minutes ago, Ace-Garageguy said:

Luck probably doesn't have anything to do with it.

I'd assume, judging from the attention you give the rest of your work, that you use product that's not expired, you probably exercise care with your mix ratios, mix very thoroughly, and you may even rough up the areas to be bonded.

If you DON'T do those things, then yes, it IS luck.

Basically, no, I don’t worry much about any of that.

I usually use epoxy in the syringes, so I let them do the mixing for me.

I do mix the epoxy well, but I never scrape, sand or rough up joints.

To this point, I’ve seen no evidence that tells me that I need to, so I don’t.

So, at this point, I guess I’ll continue to rely on my luck.

Seems to have worked pretty well for me so far.

As they say, “if it ain’t broke, don’t fix it”.

Maybe all 5 minute epoxies are not created equal?

I’m no expert, but thought I’d just add that to the mix.

 

 

 

Steve

[Ace-Garageguy]

Consumer-grade epoxies are designed to be tolerant of sloppy mixing ratios and mixing procedures, but only to a point.

The mix-ratios specified on the product should be adhered to as closely as possible.

HOWEVER...due to the poor accuracy of consumer-grade dispensing methods (you even need to pay attention to the twin-tube dispensers, as they will frequently deliver significantly more of one component than the other), extreme mix-ratio accuracy simply isn't a thing achieved by most users.

The 5-minute stuff is the weakest of any epoxy product, and any significant deviation from the specified mix-ratio only weakens the stuff further.

(I've used it myself, and allowed my employees to use it for temporary fixturing ONLY, specifically because it's so weak and easily removable)

I've watched countless people using the stuff , measure it out fairly accurately, but then fail to thoroughly mix everything they've squeezed out, getting in a hurry to slop it on whatever they're doing before it starts to "kick"...for what seemed to them good reason.

Any epoxy applied once it's begun to polymerize will NOT develop its designed adhesive strength, and can cause subsequent joint failure.

Elevated temperatures accelerate the "kick" even more, so there are multiple failure points just waiting to bite anyone who uses it.

Used reasonably carefully, quality 5-minute stuff is fine for static models.

But compared to the high-performance aerospace products I have access to, it is garbage.

EDIT: But y'all can do anything you want. I just like to make out I'm a big-shot know-it-all.

 

Edited January 28 by Ace-Garageguy

[StevenGuthmiller]

20 minutes ago, Ace-Garageguy said:

Consumer-grade epoxies are designed to be tolerant of sloppy mixing ratios and mixing procedures, but only to a point.

The mix-ratios specified on the product should be adhered to as closely as possible.

HOWEVER...due to the poor accuracy of consumer-grade dispensing methods (you even need to pay attention to the twin-tube dispensers, as they will frequently deliver significantly more of one component than the other), extreme mix-ratio accuracy simply isn't a thing achieved by most users.

The 5-minute stuff is the weakest of any epoxy product, and any significant deviation from the specified mix-ratio only weakens the stuff further.

(I've used it myself, and allowed my employees to use it for temporary fixturing ONLY, specifically because it's so weak and easily removable)

I've watched countless people using the stuff , measure it out fairly accurately, but then fail to thoroughly mix everything they've squeezed out, getting in a hurry to slop it on whatever they're doing before it starts to "kick"...for what seemed to them good reason.

Any epoxy applied once it's begun to polymerize will NOT develop its designed adhesive strength, and can cause subsequent joint failure.

Elevated temperatures accelerate the "kick" even more, so there are multiple failure points just waiting to bite anyone who uses it.

Used reasonably carefully, quality 5-minute stuff is fine for static models.

But compared to the high-performance aerospace products I have access to, it is garbage.

EDIT: But y'all can do anything you want. I just like to make out I'm a big-shot know-it-all.

 

I understand that you probably have a lot more experience with these kinds of things than I do Bill, without a doubt, but we are just building static models.

”High performance aerospace products” seem to be maybe just a little bit of overkill for holding on a 1/25th scale hubcap.

But, as you say, “people can use whatever works for them”.

In the end, I can’t tell you what caused Ferby’s problem.

All that I can say is that outside of a MEK glue for fusing bare plastic, and Elmer’s for applying embossing powder for carpets, the only other glue I use for all of my assembly jobs, from gluing in engines and chassis, to gluing on window cranks and door lock buttons, is JB Weld “Clear Weld”, and so far, I haven’t had a single issue with adhesion, whether it be 10 days, or 10 years later.

I even use it for gluing in glass!

That said, anybody who’s reading this thread is probably going to be much better off following Bill’s advice than mine, cause seriously, what the hell do I know? 😁

 

 

Steve

[NOBLNG]

46 minutes ago, Ace-Garageguy said:

I've watched countless people using the stuff , measure it out fairly accurately, but then fail to thoroughly mix everything they've squeezed out, getting in a hurry to slop it on whatever they're doing before it starts to "kick"...for what seemed to them good reason.

You think it’s tough getting 5 minute epoxy mixed well enough before it kicks….try using this stuff.🤯

P.S. I don’t recommend it.

Edited January 28 by NOBLNG

[Ace-Garageguy]

41 minutes ago, StevenGuthmiller said:

”High performance aerospace products” seem to be maybe just a little bit of overkill for holding on a 1/25th scale hubcap.

Hmmmmm... I use white glue or rubber cement for hubcaps, because it keeps low-stressed things stuck, and comes off easily should I ever decide to change the look of a build...but that's just me. 

I use the epoxy I use because I almost always have some that's gone out of date and can no longer be used safely on aircraft. The typical use-by window on my aircraft stuff is six months to 24, depending on the exact goo, in unopened containers.

There's a reason aviation epoxies are often date-coded, and that's because performance of any epoxies deteriorates with time.

I have some MGS 285 resin that's now 10 years out of date, and there's no way on dog's green Earth I'd use it on anything important, its cure time and hardness and adhesion are noticeably different than fresh material, and it's still so much better than anything in the hardware store or hobby shop, there's simply no comparison.

Consumer-grade epoxies aren't all that terrifically strong to start with, and age-out can make them useless in much less time.

Again...whatever works for you, fine.     I   d o n ' t    c a r e .

But paying attention to details like shelf-life and mixing and roughing mating surfaces can't hurt, and can very possibly ensure problems like the OP is having don't crop up.  

 

 

Edited January 28 by Ace-Garageguy
TYPO

[Ferbz]

Lots of good information that I can glean here, thanks everyone! I'm pretty 'OCD' about nailing the right amounts to mix. My OCD even extends to making sure I've mixed the two really well before applying, but looking back I think my problem might be a combo of things: I use so little epoxy at a time that I never use up even the smallest squeeze bottles. So I keep using them even tho I start to feel more and more resistance when I squeeze them to dispense the amounts that I need. I'm also cheap, thus I tend to resist buying fresh bottles maybe more often than I should 🤪 My 'cheapness' also extends to the fact that I'll buy the cheaper hobby store epoxy rather than the better hardware store brands. I also don't sand/scuff my parts before using epoxy. It's not always possible as some parts are just too small, but I can see where this could've benefitted the adhesion of some of my assemblies. I've been at this hobby for quite some time but it still amazes me how there is always SO much to improve on and learn about technique, materials, etc!

[Chariots of Fire]

I've tried the stuff that comes in a combined tube for A and B.  Never worked out that well because it was difficult to push out equal amounts.  I ended up cutting them apart.  

I note some of you don't like CA and tend to use other adhesives exclusively.  Each of us has found through experience what seems to work best.  As for me I work almost entirely with CA, using epoxy in those cases where I want some time to adjust or place parts.  Clear Gorilla glue works well with headlights, if used sparingly, but it takes a while for it to set up.  

Lastly, about all small parts get pinned as well as glued in place.  It's almost a necessity especially if parts are to be added after painting.  Gluing exclusively to painted surfaces almost guarantees that at some point the part will come off.

[TonyK]

I refuse to use those combined tubes with the push bar for many reasons as some were mentioned above. The little separate tubes became hard to find so I bought the Bob Smith brand at Hobby Lobby and have been real happy with it.

I'm very attentive to getting equal amounts out and very attentive to mixing it well and it works out well for me. You do have to be smart about the surface you're using it on and what you're trying to glue together.

I use CA glue some but only on very little parts that aren't going to be strained or require strength to support anything.

[StevenGuthmiller]

3 hours ago, Chariots of Fire said:

I've tried the stuff that comes in a combined tube for A and B.  Never worked out that well because it was difficult to push out equal amounts.  I ended up cutting them apart.  

I note some of you don't like CA and tend to use other adhesives exclusively.  Each of us has found through experience what seems to work best.  As for me I work almost entirely with CA, using epoxy in those cases where I want some time to adjust or place parts.  Clear Gorilla glue works well with headlights, if used sparingly, but it takes a while for it to set up.  

Lastly, about all small parts get pinned as well as glued in place.  It's almost a necessity especially if parts are to be added after painting.  Gluing exclusively to painted surfaces almost guarantees that at some point the part will come off.

I pin small parts as well, but not in every circumstance.

Only where I feel that extra strength will be needed for whatever reason, such as door handles, mirrors, antennas, and occasionally some engine parts that may have to endure some stress, (ie, pulleys, etc, where a belt may put extra stress on the parts)

Otherwise, I’ve found the epoxy that I use to be far superior in bond to nearly any other glue I’ve used over the years, at least initially.

As a matter of fact, I’ve had the occasion arise where I’ve had to take something apart that was assembled with epoxy, and let me tell you, it’s been a real bugger to get them apart in every case!

 

 

 

Steve

[Claude Thibodeau]

Hi!

I've had good results on 1/1 street rod builds, using "marine expoxy", sold by an established shop that deals with leisure boaters. It works great, never broke a joint in 15 years, on cars that customers use extensively, BUT... The mixing is absolutely UNFORGIVING. Out of proportion= never hardening goo.

I agree with ACE: the best stuff requires extreme care, precision mixing, and utmost cleanliness. Hardware stuff is just a compromise...

CT

[Bugatti Fan]

I have had no trouble with 2 part epoxy adhesives over the years regardless of whether slow or fast setting, proprietary or store brands.   Preparation of the parts to be glued I find is generally the key to a good bond.

I have used proprietary brands like Devcon, Araldite etc. Found them to be no better than store's own brands from my own experience for the sort of stuff we use it for as model makers.

My guess is that there are just a few companies with the expertise and geared up to make this type of adhesive and reckon that the store brands in all probability are made by those big companies.

Bill mentioned grades that are specifically formulated and made for industry, but those products would not be generally available to Joe Public, so I have no experience of how they perform.

I just wish that there was a syringe type made with precision nozzles for application of very small even amounts. The ones I have used need a cut made to unseal them, but the diameter of the holes exposed are generally a bit too big for precise application of very small mix quantities.

Edited January 29 by Bugatti Fan

[bobss396]

If you have a good digital scale, you can get both parts dispensed equally. I generally use my "eye-crometer". 

In the past I used only a dab to hold in glass. At work we had those bipax epoxies in small packages, it came with a divider that was removed, knead the 2 parts and go to town with it. We had a shelf with expired items and we helped ourselves. I never saw any of that fail.

Bigger amounts came in cans like Bondmaster 777. That was purple in color and smelled like peanut butter.

We had a damaged concrete step, maintenance used the 777 on it, it had to be there for 15 years and withstood thousands of footsteps each day.

[StevenGuthmiller]

13 hours ago, Claude Thibodeau said:

Hi!

I've had good results on 1/1 street rod builds, using "marine expoxy", sold by an established shop that deals with leisure boaters. It works great, never broke a joint in 15 years, on cars that customers use extensively, BUT... The mixing is absolutely UNFORGIVING. Out of proportion= never hardening goo.

I agree with ACE: the best stuff requires extreme care, precision mixing, and utmost cleanliness. Hardware stuff is just a compromise...

CT

Isn’t there something to be said for ease of use?

Everyone keeps saying that the “hardware store” stuff is a compromise, yet they also talk about how finicky the “good” stuff is to deal with.

Personally, I’d rather have a little less bond than to have to break out the scales to be certain that the mixture is correct.

Again, I have yet to see any compromised bond even once in all of the years that I’ve been using the JB Weld product that I use.

I understand that an argument could be made for a better epoxy solution, but before one can be convinced, one has to be shown evidence that what they’re using is inferior for the application that they’re using it for.

I remember having a similar discussion on this board some time ago, and if I remember correctly, I put together a video experiment to show what type of bond you will get with the product that I’m using.

I’ll have to try to dig it up and post it again.

Of course this is not to say that there couldn’t be deterioration of the bond over time, but really......who knows.

If anyone has factual evidence of that to show us, rather than just conjecture, I would be quite happy to see it.

 

 

 

Steve

[Ace-Garageguy]

1 hour ago, StevenGuthmiller said:

Isn’t there something to be said for ease of use?

Everyone keeps saying that the “hardware store” stuff is a compromise, yet they also talk about how finicky the “good” stuff is to deal with.

Personally, I’d rather have a little less bond than to have to break out the scales to be certain that the mixture is correct.

Again, I have yet to see any compromised bond even once in all of the years that I’ve been using the JB Weld product that I use.

I understand that an argument could be made for a better epoxy solution, but before one can be convinced, one has to be shown evidence that what they’re using is inferior for the application that they’re using it for.

I remember having a similar discussion on this board some time ago, and if I remember correctly, I put together a video experiment to show what type of bond you will get with the product that I’m using.

I’ll have to try to dig it up and post it again.

Of course this is not to say that there couldn’t be deterioration of the bond over time, but really......who knows.

If anyone has factual evidence of that to show us, rather than just conjecture, I would be quite happy to see it.

I don't understand what you're arguing about.

YOU...and anyone else...can CHOOSE to use anything you want, including unicorn snot or Cheez Whiz if that works for you.

But there are those of us who have extensive knowledge about adhesives, have access to high performance materials, and CHOOSE to use them...even if they require 2 or 3 whole extra minutes to measure on a scale.

Hardware-store epoxies are moderately good adhesives that are relatively easy to use, appeal to the average Joe, and used carefully are perfectly adequate for most static modeling uses.

And poor mixing and/or application procedures, or old material, are the main causes of problems with the stuff. That is the simple unvarnished truth. I don't understand why the truth is disputed, or at least seems to ruffle people's feathers.

However, I have made multiple posts and started threads showing mold-making and almost-scale-thickness fiberglass parts that are MUCH stronger than styrene, and that are just flat impossible to do with almost any consumer-grade epoxy.

When one has access to a very high performance epoxy product, why wouldn't one use it for everything as appropriate?

NOTE: I personally do not use epoxies for general assembly, unless I need to bond dissimilar materials that other adhesives aren't good for...like brass and aluminum to plastic. I use solvent glues wherever appropriate, and usually some variety of white glue (PVA) for clear parts, chrome parts, pinned parts, or anything I might possibly want to dissassemble in the future.

EDIT: One thing that hasn't been mentioned yet is that fully-cured epoxies DO degrade under prolonged exposure to UV light.

If a model car assembled with tiny dabs of epoxy and sitting in sunlight for a long time falls apart, well, no surprise there.

Degradation of epoxies under UV exposure is well known in aviation, even light reflected UP from the runway under a plane can cause damage...and precautions are taken to guard against it.

 

Edited January 29 by Ace-Garageguy

[StevenGuthmiller]

20 minutes ago, Ace-Garageguy said:

I don't understand what you're arguing about.

YOU...and anyone else...can CHOOSE to use anything you want, including unicorn snot or Cheez Whiz if that works for you.

But there are those of us who have extensive knowledge about adhesives, have access to high performance materials, and CHOOSE to use them.

Hardware-store epoxies are mediocre adhesives that are relatively easy to use, appeal to the average Joe, and used carefully are perfectly adequate for most static modeling uses.

And poor mixing and/or application procedures, or old material, are the cause of problems with the stuff. That is simply the unvarnished truth. I don't understand why the truth is disputed.

However, I have made multiple posts and started threads showing mold-making and almost-scale-thickness fiberglass parts that are MUCH stronger than styrene, and that are simply impossible to do with almost all consumer-grade epoxies.

When one has access to a very high performance epoxy product, why wouldn't one use it for everything?

EDIT: One thing that hasn't been mentioned yet is that fully-cured epoxies DO degrade under prolonged exposure to UV light.

If a model car assembled with epoxy and sitting in sunlight for a long time falls apart, well, no surprise there.

Degradation of epoxies under UV exposure is well known in aviation, and even light reflected UP from the runway under a plane can cause damage...and precautions are taken to guard against it.

I suppose you could say that I’m “countering” the insinuation that a material that’s available through a hardware or auto parts store is by default, “In a word, Garbage”, or is “just a compromise”.

If it does what it’s supposed to do for our particular purposes, and there’s no evidence of later failure, which I have yet to see, then I’m not sure what makes it a compromise or garbage.

I , like yourself, don’t give two sh*ts what product anybody wants to use for whatever purpose, but it does chap my backside just a little bit when because that product happens to not be up to the “standards” of some, that they’re therefore “garbage”.

That’s all.

 

 

Steve